The tread portion of a pneumatic tire generally comprises a plurality of circumferentially and laterally extending grooves defining ground engaging tread elements, the elements being in the form of blocks or ribs or combinations thereof. The particular size and shape of the tread elements contribute significantly to the overall performance of the tire and are for that reason designed to achieve the desired tire characteristics. When a tire is unworn, the relative high tread depth yields relatively low tread stiffness. However, as the tread is worn and the tread depth reduced, the tread stiffness is increased.
In addition to the grooves provided in the tread configuration, a tire tread is often provided with sipes. A sipe is a groove having a width in the range of about 0.1% to about 1% of the tread width, i.e. the arc length of the tread surface in the axial direction. The sipe tends to close when it is located in the tire footprint at zero speed and under normal load and pressure. Sipes are typically formed by steel blades inserted into a cast or machined mold or tread ring. In general, siping of conventional construction, i.e, a straight or slight curved sipe of only two dimensions, will reduce the stiffness of the tread elements in which the sipe is located.
Sipes are placed in tread elements to affect a variety of tire characteristics. One such characteristic is dry braking performance. Dry braking performance is increased with increased tread stiffness; likewise dry braking performance is decreased with reduced tread stiffness. Another tire characteristic is wet road performance. The above discussed variation in tread stiffness during the life of the tire affects a tire's wet performance characteristics as a relatively low tread stiffness is better for wet performance while a relatively high tread stiffness, in comparison, reduces the wet performance of the worn tire. This can create conflicting needs in a sipe construction.
JP 4-353431 discloses a blade; however, all of the blades disclosed therein are branched with each branch has the same configuration along the depth of the sipe and would not create a sipe that address the above conflicting characteristics.